Arrangement for stabilizing a web

ABSTRACT

The object of the invention is an arrangement for stabilizing a paper web ( 3 ) in a paper machine, which arrangement comprises at least three cylinders ( 4, 5, 6 ) which have been arranged so that a pocket space is formed between them, a blow box ( 7 ) arranged in the pocket space, which blow box has a blow nozzle ( 12 ), in which a nozzle slot ( 19 ) has been arranged, a separate wall ( 10 ), substantially in the direction of the blow box ( 7 ), which wall has a first edge and a second edge that are substantially parallel, which has been attached from its first edge to the blow box ( 7 ), whose height in the travelling direction of the paper web ( 3 ) is 25-300% of the height of the blow box ( 7 ) in the travelling direction of the paper web ( 3 ), in the second edge of which wall there has been arranged a boundary layer air doctor ( 15 ), which extends substantially unto the surface of the cylinder ( 4, 5, 6 ), and which wall ( 10 ) has been attached to the blow box ( 7 ) so that the blow box ( 7 ) and the wall ( 10 ) form a space in the area between the opening nip ( 8 ) and the closing nip ( 9 ) following it, into which space an underpressure can be arranged in order to support the paper web ( 3 ) towards the fabric ( 2 ) in the area between said nips ( 8, 9 ).

The invention relates to an arrangement for stabilizing a paper web in apaper machine or the like, in which the paper web is dried at least withthe aid of cylinders and in which the paper web is kept supportedtowards the fabric in the area between the cylinders, i.e. in a pocketspace, with the aid of a blow box. The invention relates also to a papermachine.

It is known to use blow boxes to support the web towards the fabric inthe dryer section of a paper machine or the like, between the cylinders.In the publication U.S. Pat. No. 4,932,138 a blow box has beenpresented, which occupies almost the entire pocket space and in whichthere is a blow nozzle near the opening nip. No kind of an air guidebetween the lower cylinder and the blow box has been presented, exceptfor the edge seals. In the publication U.S. Pat. No. 4,669,198 onesolution using a big blow box is presented, which blow box has almostthe size of the entire half of the pocket space, and in which there isone blow opening near the opening nip, and in the lower part, almost ina vertical direction in the upper part of the cylinder, a low air guide.The presented blow box is fairly big filling almost entirely the half ofthe pocket space. A big blow box is also fairly cumbersome for differentpurposes and expensive to manufacture. In the publication U.S. Pat. No.6,155,938 a blow box placed in the pocket space has been presented, inwhich blow box the supporting of the web towards the fabric has beenarranged with the aid of a blow nozzle placed in the lower part of theblow box. In this structure the structures arranged in connection withthe lower cylinder are, however, quite complicated and difficult tomanufacture.

In the publication U.S. Pat. No. 6,189,232 a blow box has been presentedfrom which the blow is directed towards the web so that the air flowcoming along the web is prevented from drifting along with the web. Aflexible wall that has been arranged in the vicinity of the blow nozzleis also presented in the publication. Moreover, in the publication sealsare presented that have been arranged both on the inlet side and on theoutlet side of the web so that from their other ends they are attachedto the blow box and their other ends are in touch with the cylinder.

In the publication FI 110 442 a dryer section has been presented, whichin its general outlines corresponds to the solution presented in thepublication U.S. Pat. No. 6,189,232. In this publication, however, thereis only one seal that has been arranged on the outlet side of the web.In both publications this seal is very small in dimension in relation tothe dimensions of the blow box. The blow boxes are also carefully fittedin the pocket space remaining between the cylinders, in other words,their lower edges are curved following the configuration of thecylinder.

In the publication FI 76610 a solution has been presented, in which twoblow boxes have been arranged in the pocket space between the cylinders.An auxiliary wall has been arranged in both blow boxes.

The problem of the above-mentioned solutions is that they need to bebuilt separately for each paper machine, because in them the blow boxesare substantially of the same size and form as the pocket spaceremaining between the rolls or the cylinders.

The object of the invention is thus to present an arrangement inconnection with the fabric for supporting and stabilizing the web with afairly simple blow box, which would be quite small in its cross sectionand would thereby fit easily into the cylinder pocket. One main objectis to present an arrangement, in which a blow box that is fairly smallin its cross section, and so-called standard sized, could be fitted alsoto most of the old machines. Furthermore, a special object is to presentan arrangement with a low energy consumption but still with an excellentstabilizing of the web.

The object of the invention is achieved according to what is defined inthe independent claim.

The object of the invention is an arrangement for stabilizing a web in apaper machine, which arrangement comprises

-   -   at least three cylinders, which have been arranged so that a        pocket space is formed between them,    -   a blow box arranged in the pocket space, which blow box has a        blow nozzle, in which a nozzle slot has been arranged,    -   a separate wall substantially in the direction of the blow box,        -   which wall has a first edge and a second edge that are            substantially parallel,        -   which wall has been attached from its first edge to the blow            box        -   the height of which wall in the travelling direction of the            paper web is 25-300% of the height of the blow box in the            travelling direction of the paper web,        -   in the second edge of which wall a boundary layer air doctor            has been arranged, which doctor extends substantially unto            the surface of the cylinder, and            which wall has been attached to the blow box so that the            blow box and the wall form a space in the area between the            opening nip and the closing nip following it, into which            space an underpressure is arrangeable in order to support            the paper web towards the fabric in the area between said            nips.

The invention thereby relates to an arrangement in connection with thefabric for stabilizing the web in a paper machine. The arrangementaccording to the invention can naturally be used also in othercorresponding machines. The arrangement is advantageously used in thatpart of the paper machine in which the web is dried with the aid ofcylinders and possibly also with the aid of air blows. The web is keptsupported towards the fabric with the aid of a blow box in the areabetween the first cylinder and the second cylinder or the roll. Acylinder means in this patent application for example a drying cylinderor a plain, grooved or perforated roll.

According to one embodiment, the blow nozzle of the blow box has beenplaced in the travelling direction of the web so that the nozzle slot ofthe blow nozzle is substantially before the opening nip so that it blowsair away from the underpressure space. The location before the nip meansthat the nozzle slot is, at the maximum, about 200 mm above the nip,advantageously at the maximum about 50 mm above the nip. Thereby theefficiency of the blow box for controlling the paper web is great. Theblow box extends advantageously substantially on the entire width of theweb.

According to one other embodiment of the invention, the blow box hasbeen placed so that the nozzle slot of the blow nozzle is substantiallyat the opening nip. According to one further embodiment of theinvention, the blow box has been placed so that the nozzle slot of theblow nozzle is, in the travelling direction of the web, substantiallybelow the nip, e.g. at the maximum about 100 mm, advantageously at themaximum about 30 mm below the nip.

In addition, in the arrangement according to the invention, there is aseparate wall substantially in the direction of the blow box. In thedirection of the blow box means here that this wall has also beenarranged substantially on the entire width of the web. The wall hasparticularly advantageously been made of a plate-like material, wherebythe width and length of the wall are substantially greater than itsthickness. The width of the wall means here the dimension that is in thedirection of the width of the paper machine, i.e. transversely againstthe travelling direction of the paper web. Correspondingly, the heightof the wall is the dimension that is parallel to the travellingdirection of the paper web. The wall has also a first and a second edgethat are substantially parallel with each other and, furthermore, theyare substantially parallel to the lateral direction of the wall.

In the solution according to the invention, the said wall has beenattached from its first edge to the blow box. The joint hasadvantageously been made so that it can be opened. Furthermore, thejoint is advantageously tight, i.e. a sealing element known per se isadvantageously used in it. Thereby an underpressure space is formed, inwhich there is no significant spillage.

The height of the wall according to the invention in the travellingdirection of the paper web is 25-300% of the height of the blow box inthe travelling direction of the paper web. In addition, in the otheredge of the wall there has been arranged a boundary layer air doctorextending substantially unto the surface of the cylinder. “Substantiallyunto the surface of the cylinder” means here that the boundary layerdoctor and the surface of the cylinder are mainly in touch against eachother, however so that there may be e.g. a 1-2 mm gap between them. Onthe other hand, the boundary layer doctor is not pressed with a forcetowards the surface of the cylinder. This so-called boundary layer airdoctor prevents as well as possible the air flow caused by the secondcylinder or the roll towards the web in the area between the opening nipand the closing nip.

Thus, in the solution according to the invention there is a separatewall and a boundary layer air doctor attached to it. It can be said thatin some of the solutions presented in the above-mentioned publicationsthere is also a wall of this kind connected to a boundary layer airdoctor, but in them the height of this wall is very small in relation tothe height of the blow box, contrary to what is presented in thisinvention. On the other hand, the invention differs from the solutionpresented e.g. in the publication FI 76610 in that in the solutionaccording to the invention it is possible to arrange an underpressure inthe area between the opening nip and the closing nip following it.

With the solution according to the invention such an important advantageis achieved that because the said wall and the boundary layer air doctorplaced in its edge can be dimensioned so as to be suitable for eachcase, a wall and a boundary layer air doctor of the size that isnecessary in each object of use can be attached to a standard-sized blowbox. Thereby savings in costs can be attained as the manufacturing ofthe said blow box of a standard size is carried out in series productionand thus economically. The wall according to the invention, in its turn,is a plate-like product and thus more economical to manufacture that theactual blow box. Furthermore, holes that are elongated in elevationdirection can be arranged in the wall, with the aid of which holes thecombined height of the wall and the blow box can be adjusted.

Thus, in the solution according to the invention, the wall has beenconnected to the blow box so that the blow box and the wall form a spacein the area between the said opening nip and the closing nip followingit, into which space an underpressure can be arranged in order tosupport the paper web towards the fabric in the area between the saidnips. In this way, a solution is achieved, which suits not only to thenew machines but also to most old machines. In this way an advantageoussolution from the point of view of energy consumption can be achieved,in which also the stabilizing of the web succeeds well.

The height of the said wall is determined by the machine geometry.According to one embodiment of the invention, the height of the wall inthe travelling direction of the paper web is 50-150%, advantageously70-100% of the height of the blow box in the travelling direction of thepaper web. It is clear that the height of the wall with respect to theheight of the blow box is chosen on the basis of the desired totalheight. Thereby, the height of the wall can be e.g. 25-50%, 25-80%,25-100%, 25-90%, 50-200%, 50-120%, 50-250%, 70-100%, 70-120%, 150-300%,150-200% or 70-150%, as well as 25, 29, 30, 36, 42, 50, 53, 61, 65, 70,79, 75, 82, 90, 93, 100, 105, 110, 115, 120, 134, 140, 148, 159, 180,200, 247, 268 or 295% of the height of the blow box.

According to one other embodiment of the invention, the boundary layerair doctor has been arranged in the second edge of the wall via asupport element. Then the joining of the boundary layer air doctor tothe wall is made easily firm and tight. It is especially advantageous ifthe boundary layer air doctor can be replaced without removing saidsupport element or blow box from the machine, as then the replacement isa simple and a fairly quick operation. The boundary layer air doctor canbe replaced e.g. by pulling or pushing away the doctor that is in itsplace and by pulling or pushing the new doctor to its place.

With the arrangement according to the invention, an underpressure thatis at least 50 Pa lower than the normal pressure can advantageously bearranged into the space delimited by the blow box and the wall. Moreadvantageously this pressure is at least 120 Pa lower that the normalpressure.

Furthermore, in the arrangement according to the invention, it ispossible to arrange in connection with the blow box a flexible nozzlewall that bends elastically in fault situations, web breaks, and thelike, where an enlarged safety distance is needed between the cylinderand the box. This kind of a flexible nozzle wall has typically beenarranged near the blow nozzle, in the machine direction a little afterit. Advantageously the flexible nozzle wall is just above the nip. Aflexible nozzle wall means both a wall that is made of a flexiblematerial, and an element stiff as such that has been arranged so as tobe flexible e.g. with the aid of a spring or a turning joint or that hasbeen arranged so as to move around its axis or point of articulation.This kind of a flexible nozzle wall can function either with springforce or with gravitational force. One flexible nozzle wall suitable foruse in an arrangement according to the invention has been presentedbelow in connection with the description of the drawing. One othernozzle wall, known per se, also suitable for use in an arrangementaccording to the invention has been presented in the applicant's patentFI 102400.

In the vicinity of the blow nozzle there can be arranged a flexiblestrip that bends elastically if, in a fault situation foreign material,such as paper chaff or the like comes along the web. Then this foreignmaterial does not break the structures. Also the above-presented nozzlewall is able to bend elastically if foreign material comes along withthe web.

The arrangement according to the invention can be used in such machineswhose web speed is normally at the maximum 1000 m/min, even though thescope of use of the invention is typically in such applications in whichthe web speed is between 600-1400 m/min. The arrangement according tothe invention is especially useful in modernizations of old machineswhich often present also problems of space when placing big blow boxesinto the machine structures.

The boundary layer air doctor is advantageously manufactured of amaterial that is flexible to at least some degree and/or it is arrangedso that it can bend elastically. In this case it is likely that thepossibly created chaff or other foreign material does not cause damagesto the equipment.

It is recommended that the said blown air is produced by using one ormore blowers. The power required by the blowers is then quite reasonableand the channels and the equipment are fairly small in size.

Furthermore, an object of the invention is a paper machine thatcomprises an arrangement as presented above for stabilizing a paper web.

In the following, the invention is described more closely with referenceto the enclosed drawing, in which

FIG. 1 schematically and, for the sake of clarity, some what exaggeratedillustrates one runnability problem arising in paper machines,

FIG. 2 illustrates one embodiment of an arrangement according to theinvention for stabilizing a web in a paper machine and especiallysupporting of the web towards a fabric in the area between cylinderswith the aid of a blow box,

FIG. 3 schematically and enlarged illustrates the lower part of the walland the boundary layer air doctor illustrated in FIG. 2, and

FIG. 4 schematically illustrates the blow nozzle illustrated in FIG. 2.

In FIG. 1 of the drawing, one runnability problem arising in papermachines is illustrated exaggerated to some degree for the sake ofclarity, which problem concerns stabilizing of the web when no kind of ablow box is used in the pocket space. The reference mark a illustrates acylinder from which a fabric b and a paper web c move down to a lowercylinder d and further on to a cylinder e. When the fabric b and the webc are detached from the cylinder a, the web c and the fabric b oftendetach from each other, which usually causes problems. It has also oftenbeen noticed that the web c is not in touch with the fabric b at thelower cylinder d as is shown in FIG. 1.

In FIG. 2, the reference number 1 shows an arrangement according to oneembodiment of the invention in connection with a fabric 2 forstabilizing a web 3 in a paper machine or the like, in which the web 3is dried with the aid of cylinders 4, 5 and 6 and possibly also with theaid of air blows, and in which the web 3 is kept supported towards thefabric 2 in the area between the cylinders 4 and 5 with the aid of ablow box 7. The walls of the blow box 7 have most usually been formed ofa metal plate by bending and welding and/or by other joining methods.Its width in the cross direction of the web 3 is approximately the widthof the web 3 or a little more. An underpressure is arranged into a space11 formed by an opening nip 8, a closing nip 9 and a wall 10 connectedto the blow box 7 by blowing air with the aid of a blow nozzle 12 awayfrom the space 11 i.e. in the direction of an arrow 13. The air to beblown is brought to the blow nozzle 12 along a channel (not shown)arranged in the blow box 7. In the vicinity of the blow nozzle 12 therehas also been arranged a flexible nozzle wall 18. The part near the blownozzle 12 has been arranged to be able to move at least to some extentif, for some reason, impurities, e.g. a so-called paper lump or the likecomes down from higher. The blow nozzle 12 is located in the upper partof the blow box 7 some what, e.g. 5-15 cm or even more, above theopening nip 8. The use of this kind of a part that is able to bendelastically and located near the blow nozzle 12 is a technique know perse in this kind of embodiments.

The wall 10 has most suitably been formed of a plate, e.g. an aluminumplate, even though also other materials can be considered for this use.The wall 10 has been attached fairly tightly with screws or the like(not shown) from a point 14 to the front wall of the lower part of theblow box 7, i.e. to the front wall of the blow box 7 in the machinedirection. It is recommended to have in elevation direction elongatedholes (not shown) in the wall 10, with the aid of which holes anadjustment margin is achieved, which can be e.g. 3 cm. In the lower partof the wall 10 there is a boundary layer air doctor 15, which has beenmounted to a support element, i.e. a doctor support 16 in the lower partof the wall 10. The doctor 15 is flexible at least to some extent, andits lower part is quite near the surface of the cylinder 5 or in touchwith the surface of the cylinder. The height of the wall 10 is quitehigh compared to the height of the blow box 7. In one typical embodimentthe height of the blow box is about 40 cm and the height of the wall 10more than 30 cm. The cross section of the blow box 7 can be the same inseveral different applications, and the underpressure space 11 is formedby choosing a wall 10 of a height suitable for the application. Whenacting this way, the blow box 7 can be considered as a standard productand the wall 10 is simple to manufacture in pieces of different sizeaccording to need, because most usually the wall 10 is a planar piece ofplate, which is fairly simple to manufacture.

FIG. 3 illustrates more in detail the lower part of the wall 10according to this embodiment with its doctor 15. In the lower part ofthe wall 10 there is attached a doctor support 16, which has beenattached air tightly to the wall 10 with the aid of a flat seal 17. Thedoctor 15 it-self is made of a flexible material, e.g. rubber or thelike, and the entire lower part of the doctor 15 is fairly thin. In thisembodiment the doctor 15 remains in place in the doctor support 16because the cross section of the upper part of the doctor 15 is circularand the doctor support 16 has a similar structure, even though asuitable spacing is necessary for the sake of the replacement of thedoctor. It is to be noted that in the lower part of the doctor support16 there are fairly long guide surfaces in order to hold the doctor 15in place. The wall 10 is adjusted with the aid of screws or the like tosuch a height that the lower part of the doctor 15 slightly touches thesurface of the cylinder 5. Thereby leakage passing the doctor 15 isminor and a desired underpressure is easily maintained in the space 11in order to control the web 3 in the web part after the opening nip 8.The profile of the doctor 15 is such that a worn doctor is easily pulledaway and, correspondingly, a new doctor can be set in its place. Thestructure of the lower part of the wall 10, the doctor support 16 andespecially the doctor 15 can be conceived to operate especially as aso-called boundary layer air doctor, as the roll 5 causes, due to itsrotary movement, a fairly big air flow near its perimeter surface, andthe said doctor eliminates almost entirely the said air flow andespecially turbulent flows and their detrimental effects on the web 3 atthe space 11. Therefore the doctor 15 is, from its lower part, at leastalmost in touch with the cylinder 5 in order to attain an efficientboundary layer air doctor effect.

The structures also include end plates (not shown) with the aid of whichthe space 11 is fairly well closed from both edges of the web 3.Thereby, a required underpressure can be formed into the space 11 sothat, via the blow nozzle 12, it is blown air brought at the spot by theducting of the blow box 7 at least to such an extent that in the centralarea of the space 11 the air pressure is at least 50 Pa, preferably atleast 120 Pa lower that the normal air pressure. This is usually asufficient underpressure level for controlling the web 3 in the range ofinfluence of the space 11, and especially near and after the opening nip8.

FIG. 4 schematically illustrates the blow nozzle 12 shown in FIG. 2. Anozzle slot 19 and flow of air according to arrows 20 have beenillustrated in a blow nozzle according to this embodiment. In theFigure, also the flexible nozzle wall 18 has been illustrated in twodifferent positions, in its position of use (by reference number 18) andin its open position (by reference number 18′), when some foreign matterhas come along with the web. Furthermore, cylinder 4, paper web 3 andfabric 2 as well as opening nip 8 have been illustrated in the Figure.

The invention is recommended to be used not only in new machines butalso in rebuilds of old machines, both in paper and board machines. Theinvention is especially suitable for machines having a width of lessthan 6 m, even though the machine width can of course be even more thanthis. In the rebuilds of old machines the web speed is usually about1000 m/min. With the arrangement according to the invention,applications with low energy consumption are attained, and thereforerelatively small-sized and economical low-pressure blowers can be usedin the production of air.

The invention is not limited to the enclosed embodiment but severalmodifications of it can be conceived within the scope of the enclosedclaims. The reference numbers are not to be considered to limit theinvention, either.

1. An arrangement for stabilizing a paper web (3) in a paper machine,which arrangement comprises at least three cylinders (4, 5, 6), whichhave been arranged so that a pocket space is formed between them, a blowbox (7) arranged in the pocket space, which blow box has a blow nozzle(12), in which a nozzle slot (19) has been arranged, a separate wall(10) substantially in the direction of the blow box (7), which wall hasa first edge and a second edge that are substantially parallel, whichwall has been attached from its first edge to the blow box (7), theheight of which wall in the travelling direction of the paper web (3) is25-300% of the height of the blow box (7) in the travelling direction ofthe paper web (3), in the second edge of which wall a boundary layer airdoctor (15) has been arranged, which doctor extends substantially untothe surface of the cylinder (4, 5, 6), and which wall (10) has beenattached to the blow box (7) so that the blow box (7) and the wall (10)form a space in the area between the opening nip (8) and the closing nip(9) following it, into which space an underpressure is arrangeable inorder to support the paper web (3) towards the fabric (2) in the areabetween said nips (8, 9).
 2. An arrangement according to claim 1,characterized in that the height of the wall (10) in the travellingdirection of the paper web (3) is 50-150% of the height of the blow box(7) in the travelling direction of the paper web (3).
 3. An arrangementaccording to claim 2, characterized in that the height of the wall (10)in the travelling direction of the paper web (3) is 70-100% of theheight of the blow box (7) in the travelling direction of the paper web(3).
 4. An arrangement according to claim 1, characterized in that aboundary layer air doctor (15) has been arranged in the second edge ofthe wall (10) via a support element (16).
 5. An arrangement according toclaim 1, characterized in that into the space formed by the blow box (7)and the wall (10) an underpressure can be arranged that is at least 50Pa lower than the normal pressure.
 6. An arrangement according to claim1, characterized in that a flexible nozzle wall (18) has been arrangedin connection with the blow box (7).
 7. An arrangement according toclaim 1, characterized in that the boundary layer air doctor (15) hasbeen arranged to be replaceable without taking the said support element(16) and/or the said blow box (7) away from the paper machine.
 8. Anarrangement according to claim 7, characterized in that the boundarylayer air doctor (15) has been arranged to be replaceable by pulling orpushing away the boundary layer air doctor (15) that is in its place andby pulling or pushing a new boundary layer air doctor (15) to its place.9. A paper machine that comprises an arrangement according to claim 1for stabilizing a paper web.